In order to protect sheet material, in particular valuable documents it is known to weld the sheet material together with a laminating foil. Thus, the sheet material is inserted between two foil sheets forming a laminating foil, wherein the sheet material and the foil sheets are then jointly transported through the laminator. The foil sheets can also be provided as a laminating foil pouch wherein the two foil sheets are connected with each other at least at one side edge. Laminating foils of this type are known for example from DE 201 00 328 U1. It is characteristic for laminating foils that they are configured as composite foils where a transparent clear foil, e.g. made from polyester or polypropylene is provided with a heat sensitive glue layer on an inside wherein the glue layer can be made for example from EVA (ethylene vinyl acetate copolymer).
In the non-industrial sector, this means in the office and private sector laminators are typically used that are configured as table top units. Laminators of this type are known from DE 20 2009 000 903 U1. They typically have the same basic configuration with a unit housing in which a laminating unit is arranged. A pass through channel extends between an infeed opening on one side and an outlet opening on another side of the unit housing wherein the laminating unit is associated with the pass through channel. The laminating unit typically includes a pair of rollers, sometimes also several pairs of rollers which are respectively made from two laminating rollers that are arranged on top of each other forming a laminating gap. Thus, the laminating gap is configured so that the combination of sheet material and laminating foil in the laminating gap is subjected to a substantial pressure.
In hot laminators one of the laminating rollers, typically both laminating rollers are heated. When a combination of the sheet material and the laminating foil passes through the combination is additionally heated in the laminating gap. This renders the glue layer of the laminating foil gluable and provides a connection of the foil sheets with each other and with the sheet material to be encased by welding. The temperature during hot lamination is thus set so that a portion of the foil sheets which is made from the clear foil is not impaired by the heat impact.
Typically rod shaped heating modules are used for heating the laminating rollers. A laminating roller is known for example from DE 20 2011 052 223 U1 wherein a heating module is provided from a PTC (positive temperature coefficient) heating rod that is enveloped by an insulating foil and installed in a central axial pass through opening of a heat conducting and temperature resistant roller element of the laminating roller. However for example also resistance heating rods are known in the art. A PTC heating rod has temperature resistance properties which provide decreased heating power with increasing temperature, this means the PTC heating rod is substantially self-regulating. In PTC heating rods of this type therefore external control or regulation or overheating protection can be substantially omitted. It is another advantage of the heating rods of the type recited supra that laminating foils with different thickness can be laminated with the same temperature since the PTC heating rod regulates the thermal energy according to the heat requirement self-acting this means less thermal energy is provided for a thinner foil, than for a thicker foil.
In the laminating roller that is known from DE 20 2011 052 223 U1 the roller body is made from two roller core elements which are assembled to form the roller body. Assembling the two components does not provide a perfectly cylindrical outer surface of the roller body without edges or protrusions. Such surface, however, would be necessary for example to pull a hollow cylindrical hose as a roller cover onto the roller body. When a hose is pulled onto the roller body that is known from DE 20 2011 052 223 U1 then wedging of the hose at edges or protrusions at the outer surface of the roller body occurs quite frequently. For this reason, among others, applying a roller cover is often omitted in known devices. Instead the roller body is encased with the material of the roller cover after joining. Since an accurate and even encasement through injection molding is not always possible scrap rates in an order to magnitude of 17% occur during the production of laminating rollers. It is difficult in particular to apply a roller cover with constant thickness through injection molding when there are edges or protrusions at an outside of the roller body.